This invention relates generally to a method facilitating the introduction of a piercing rod into a taphole of a shaft furnace before complete hardening of a taphole clay which has previously been injected into the hole. More particularly, this invention relates to a method in which the introduction is carried out without a hammer, under the effect of an axial thrust exerted by a powerful drive means on the rod.
This invention relates to the now well-known "lost rod" method, in which, after having closed the taphole with a taphole clay, a metal rod is driven into the latter before it hardens completely. The opening of the taphole is produced by extracting, at the desired moment, the rod from the hardened taphole clay.
Most often, the machines used for implementing this method comprise a powerful bidirectional pneumatic hammer for developing the energy necessary for the introduction and for the extraction of the rod. A power hammer, as is used on these machines, is not without its drawbacks. First, these hammers exert considerable stress and vibration on the equipment, in particular on the rod-coupling clamp, which is, as a result, subjected to rapid wear. It is also extremely noisy, and often does not conform to the ever stricter standards that are aimed at reducing the noise level in an industrial environment.
The aforementioned reasons have excellerated the tendency toward doing away with the bidirectional hammer. The next generation of piercing machines work with powerful drive means in order to drive in and to extract the rod forcefully, that is to say without a hammer.
The forceful extraction of the piercing rod proves fairly simple. In fact, it is necessary only to fix a coupling, for example a clamp, firmly to the free end of the rod and to push back this coupling axially in the extension of the rod, under the action of a powerful drive means, for example a jack or a hydraulic motor. The rod will then be forcefully extracted from the hardened taphole clay, under the effect of a simple axial pulling force, silently and without vibrations.
The operation for forceful introduction of the rod is, however, much more difficult. In fact, it is not sufficient to apply a strong axial thrust to one end of the rod, in order to drive the other end into the hardening taphole clay. In view of the long length of the rod and the rapid hardening of the taphole clay previously introduced into the taphole, the rod would rapidly be subjected to buckling and could become blocked in the taphole; unless special precautions have been taken, (i.e.), reducing the equivalent buckling length of the rod. It should be noted that the latter is a fictional length which takes into account the affect of the mode of fastening of the rod and of the mode of application of the force on the tendency to buckle.
This equivalent buckling length may, for example, be reduced by guiding the rod in the axis of the force applied using intermediate guides. A similar effect is obtained by applying the axial thrust not at the free end of the rod, but, with the aid of a reciprocating movement of a clamp, at a relatively small distance from the taphole. This method was proposed for the first time in the Luxembourg Patent Specification LU-87 915 which corresponds to U.S. application Ser. No. 862,487 filed Apr. 2, 1992, and which is assigned to the assignee hereof, all of the contents of which are incorporated herein by reference.
It will be appreciated that a reduction in the axial force required to introduce the rod into the taphole clay would both reduce the risk of buckling and facilitate (speed-up) the insertion of the rod into the taphole clay.
An object of the present invention is to provide a method for introducing the rod into the rapidly hardening taphole clay which allows the resistance to penetration of the rod into the taphole clay to be reduced.